The present invention relates to a process for separation of hafnium tetrachloride from zirconium tetrachloride which produces zirconium tetrachloride with a low hafnium content suitable for use as a raw material for the production of reactor grade zirconium metal and hafnium tetrachloride with a high hafnium content with high yield.
Zirconium ore contains generally about 2.about.4 wt % of hafnium. As hafnium tetrachloride is slightly more stable than zirconium tetrachloride for the chlorination reaction of both oxides, the concentration of hafnium tetrachloride in the chlorides is almost the same as that of the ore. Zirconium tetrachloride containing hafnium tetrachloride in natural ratio is used as a starting material for production of zirconium and hafnium metals. As the thermal neutron absorption cross section of hafnium is very high, a hafnium content in zirconium used for a reactor must be less than 100 ppm. Besides, hafnium is an excellent control material for a reactor because of high absorption of neutron.
Conventionally in commercial processes for separation of hafnium from zirconium there is a solvent extraction process which uses zirconium tetrachloride as a starting material and hexon as a solvent (J. W. Ramsey, W. K. Whitson Jr. Production of zirconium at Y-12, AEC Report Y-817, Oct. 12, 1951) and a distillation process in which vapors of zirconium tetrachloride and hafnium tetrachloride are absorbed selectively by salts such as aluminum chloride and are separated continuously from each other in a distilling column (French Patent No. 7340395, Japanese Patent Publication No. 20279 of 1978, Japanese Patent Provisional Publication No. 184732 of 1984).
In the former the running cost is high owing to its low recovery of solvent and chemicals used. In the latter the running cost is low, however, a huge distiller is required and its maintenance cost is high. A patent somewhat related to the present invention is U.S. Pat. No. 2,791,485 in which zirconium tetrachloride is reduced to trichloride for separation by the use of a reducing agent, but this process is not yet commercialized owing to the difficulty in separation of the reducing agent.